156 SHOULDER-GIRDLE AND BREAST-BONE. 



Palaraedeas on the other. But the true Charadii and Tringa are of the highest importance 

 to the morphologist, as they evidently are the radical or embryonic types, from whence we 

 may conceive whole groups of Amphibious and Water Birds to have arisen by special modifi- 

 cation. The Pelecaninse seem to be another fundamental group, and perhaps the Rails also ; 

 but of this I am doubtful, for they have strong marks of belonging to a derived type. 



Both in the skull and in the structure of the thorax the typical Pluvialinse present very 

 important permanent characters ; and these characters are either lost or modified in the metamor- 

 phosis which the derived types undergo. They are but little removed from what is typically 

 Struthious in the characters of the skull ; but to these new ones are superadded, for instance, the 

 large " lateral occipital fenestrae," and the more or less perfect transpalatine angle to the palatine 

 bone ; the perfectly ornithic maxillaries, which, however, do not meet at the mid-line ; and the 

 typical development of the " basi-temporals " and eustachian grooves. So that, as to the skull, the 

 Pluvialines are very much more typical than the Struthionidse ; yet they nevertheless keep 

 in, a very embryonic condition throughout their life. The Shoulder-girdle and Sternum of the 

 Pluvialinse are typically ornithic; but these parts are not modified to the same extent as in 

 the surrounding and, as it were, nobler types. I am able to give the condition of the Shoulder- 

 girdle of Fanettus cristatus at the end of the first third of the incubating period, before it 

 has lost the whole of those simple characters which are persistent in the Ostriches, and the 

 Sternum of the same embryo which is in a much less advanced stage than that which is 

 persistent in the Ostrich-tribe (see Plate XV, fig. 1, magnified seven diameters; figs. 2 and 3, 

 twenty diameters). The scapula (sc.) and the coracoid (cr.) are bent on each other at an obtuse 

 angle ; the bony shaft of each invests about a third, in the middle, and a cleft has appeared 

 opposite the glenoid cavity (gl.) ; neither of these bars have the elegant form of the fully formed 

 bones ; they are more outspread and Reptilian. The meso-scapular and prae-coracoid segment 

 form one piece of soft cartilage constricted at the middle (see figs. 1 and 3) ; a delicate bony bar, 

 the clavicle (cl.), is creeping into this mass above, and below has commenced to coalesce with its 

 fellow (see figs. 1 and 2, cl.) ; the interclavicle cannot be traced at this early stage. The Sternum 

 is in a most instructive condition ; its structure is softer than that of the Shoulder-girdle, and its 

 two halves have not united ; in front we see how the anterior sternal " notch " is formed ; and 

 behind we have the long " xiphisternal horns " (x. st.). The keel has not begun to form, and all the 

 "rostral" region is absent, as also the "middle and intermediate xiphisternals." The six sternal 

 ribs are not segmented off close to the sternal margin, but at some distance ; and these sternal 

 pedicles become converted into the transverse, elevated condyles. The coracoid grooves (cr. g.) 

 are in the very best stage for the confutation of all transcendentalism with regard to the Shoulder- 

 girdle. The inner lip is wholly within the epicoracoid flap, and the sigmoid outer lip is seen to 

 be far behind it, and to be merely a ledge-like outgrowth, which grows forwards and outwards to 

 abut against the embracing epicoracoid. The epicoracoid keeps its primordial relation to the 

 inner lip of the groove, and becomes underlapped by the outer lip ; thus, also, the sternal keel, 

 as an outgrowth, comes to be external to the Shoulder-girdle. But the sternal ribs are here 

 caught in the very act of breaking away from their common outspread terminal plate the sternal 

 moiety ; they are thus related to the Sternum necessarily ; and if the somatomic differentiation 

 had been more potent, the Sternum would have been composed of succeeding segments from 

 the first : all its after-attempts at subdivision are feeble in the Bird ; not so in the Mammal, 

 however. 



